Polychloropyridines are valuable intermedlates in the production of a wide variety of agricultural insecticides, herbicides, fungicide, and many other useful materials. Several polychloropyridines have been produced commercially and a number of processes for their production have been described. These known processes generally involve the chlorination of pyridine or a compound containing a pyridine nucleus. Methods for the chlorination of pyridine to polychloropyridines are revealed, for example, in U.S. Pat. Nos. 3,732,230 and 3,420,833. The chlorination of akyl pyridines in the vapor phase to obtain pentachloropyridine is further taught in U.S. Pat. No. 3,420,833. The chlorination in the liquid phase of alpha-picoline, beta-picoline, and 3,5-lutidine to obtain certain polychloropyridines is shown in U.S. Pat. Nos. 4,577,027, 4,483,993, and 4,507,486, respectively. Certain metal halide catalysts are sometimes employed ln these processes. 2,6-Dichloropyridine is converted to 2,3,5,6-tetrachloropyridine and pentachloropyridine by liquid phase chlorination in the presence of selected metal halide catalysts according to U.S. Pat. No. 3,538,100. The liquid phase chlorination of various chlorinated (trichloromethyl)pyridines to obtain certain polychloropyridines is discussed in U.S. Pat. Nos. 3,186,994, 4,256,894, 4,563,531, and 4,483,993. The use of uv light and of specific metal halide catalysts is optionally employed in some of these processes.
The present invention relates to the preparation of a select class of polychloropyridines by the chlorination of certain polychloro-2,3-lutidines.